TUESDAY, April 28, 2015 (HealthDay News) -- Girls on the milder end of the autism spectrum tend to be diagnosed at a later age than boys, possibly because their symptoms are less severe, a new study has found.

Doctors diagnosed girls with Asperger's syndrome and pervasive developmental disorder months later than boys who had the same disorders, according to the study.

This appears to be because mild autism in girls takes the form of social awkwardness, and is less readily apparent than the physical symptoms that boys with mild autism display, said study co-author Dr. Paul Lipkin, director of the Interactive Autism Network at Kennedy Krieger Institute in Baltimore.

"The girls' problems seemed greatest in terms of social interpretation, which is obviously much more subtle and less apparent," Lipkin said. "Boys were worse than the girls in areas that involve repetitive behaviors or unusual mannerisms. The problems the boys were having were overt and more readily recognized."

Autism spectrum disorders are a group of developmental problems that can cause significant social, communication and behavioral challenges, according to the U.S. Centers for Disease Control and Prevention. The CDC estimates that one in 68 U.S. children has an autism spectrum disorder.

Results of the new study were scheduled to be presented Tuesday at the Pediatric Academic Societies annual meeting in San Diego. Findings presented at meetings are generally considered preliminary until they've been published in a peer-reviewed journal.

Autism is found much more often in boys than in girls, which has raised the question of whether some girls with autism go undiagnosed.

"We know there is this unbalanced ratio, with about four times as many boys being diagnosed as girls, and we don't know why that is," said Dr. Paul Wang, senior vice president of medical research at Autism Speaks, an autism advocacy organization.

This delay in diagnosis could mean a tougher road for girls with autism, since children with autism do best when the disorder is caught and treated early, Wang said.

To explore this gender difference, researchers analyzed data from the Interactive Autism Network, an online registry of almost 50,000 individuals and family members affected by autism spectrum disorder.

In the registry, age of first diagnosis was available for almost 10,000 children, and more than 5,100 had completed a test called the Social Responsiveness Scale, which identifies the presence and severity of social impairment.

Researchers found that boys and girls with "classic" severe autism received a diagnosis at about the same time, Lipkin said.

But girls with pervasive developmental disorder, an autism condition that impacts the development of many basic skills, tended to receive a diagnosis at an average age of 4 years, compared to 3.8 years for boys.

This also was the case with girls diagnosed with Asperger's syndrome. Girls received a diagnosis at an average age of 7.6 years for the condition, which affects language and behavioral development, versus 7.1 years for boys.

Researchers also found that girls exhibited markedly different autism symptoms than boys.

Girls struggled more with the ability to recognize social cues and interact with others. They had trouble interpreting requests made of them, took things too literally, struggled to understand jokes and couldn't read into people's tone of voice or facial expressions, Lipkin said.

On the other hand, boys exhibited much more physical symptoms. They engaged in repetitive behaviors, like turning the wheel of a toy around and around for extended periods, as well as unusual mannerisms such as flapping their hands, Lipkin said.

Current autism research is delving deeper into these differences between boys and girls, to better understand them and improve diagnosis for girls, Wang said

For example, some researchers are following babies born into families where there's already someone with autism, which means that they have a higher risk of developing the disorder.

"You can start following them at a very young age to see what's happening with them," Wang said. "That's the kind of research that will hopefully shed some light on this."

In the meantime, parents must not overlook potential symptoms in girls, and doctors should keep a close eye on any girl who seems to have developmental issues, Wang said.

"Parents really need to be sensitive toward a child's social development and not expect girls to have the same problems as the boys," he said. "If they suspect something's the matter, they really need to bring this to the attention of a health care professional or someone in the child's school so it can be investigated in greater depth."